Conventionally, there is provided a fine particle feeder, which is composed as follows. There is provided a fine particle tank in which fine particles are stored, and a lower portion of the fine particle tank is connected with an air feed pipe into which air at high pressure is fed. An internal space of the fine particle tank is partitioned into three sections in the vertical direction. Communicating ports are formed on a top and a bottom surface of the intermediate section. Opening and closing valves are respectively arranged in the communicating ports. When the upper opening and closing valve is opened, the fine particles are filled from the upper section into the intermediate section. After the upper opening and closing valve has been closed, the lower opening and closing valve is opened, so that the fine particles are discharged from the intermediate section into the lower section, and the fine particles are made to drop from the lower section into the lower air feed pipe, so that the fine particles are mixed with air of high pressure and transported together with air of high pressure. However, the above fine particle feeder is disadvantageous in that the upper and the lower opening and closing valve can not be simultaneously opened because the inside of the entire fine particle tank must not be put into a state of positive pressure by air of high pressure in the air feed pipe.
Therefore, while the fine particles filled in the intermediate section are being discharged into the lower section, it is impossible to open the upper opening and closing valve and fill the intermediate section with the fine particles sent from the upper section. As a result, when all fine particles filled in the intermediate section has been discharged into the lower section, it is impossible to discharge the fine particles into the lower section until the filling of the fine particles from the upper section into the intermediate section is finished. Therefore, the fine particles are intermittently fed into the air feed pipe, that is, it is impossible to feed the fine particles continuously.
In order to feed the fine particles continuously, the following arrangement may be provided. The intermediate section of the fine particle tank is extended, so that a quantity of fine particles discharged to the lower section is increased. Before all fine particles are discharged into the air feed pipe, new fine particles are filled in the intermediate space so that discharging stand by state is established. However, the above arrangement is disadvantageous in that it is necessary to extend volumes of the intermediate and the lower section, and the size of the fine particle tank is increased. As a result, the manufacturing cost is raised and further it becomes difficult to ensure the installation space, and furthermore, it becomes difficult to properly conduct maintenance on the device.
On the other hand, the conventional shot blasting device conducts polishing on a surface to be polished as follows. Particle-shaped grit fed from the fine particle feeder is sent into a high pressure air line and transported pneumatically to a blasting device for shot blasting attached to an end of the high pressure air line. Thus transported grit is strongly blasted out from the blasting device and made to collide with a surface to be polished, so that rust and coating can be peeled off from the surface to be polished. However, when the fine particle feeder in this shot blasting device is composed of the aforementioned conventional fine particle feeder, the size of the fine particle feeder is extended in the same manner as that described above, and further it is difficult to feed grit smoothly because of air pressure. Furthermore, in the conventional shot blasting device, it is difficult to recycle grit which has been used once.